Internal combustion engine comprising a reducing agent production unit and operating method therefor

ABSTRACT

An internal combustion engine with a reducing agent-generating unit for generation of an H 2 -containing and/or NH 3 -containing reducing gas, which can be added to an exhaust gas line upstream from an NO x  reducing catalytic converter, and a procedure for the operation of such an internal combustion engine are proposed. The reducing agent-generating unit has an NO x  generation step and an H 2  generation step in serial arrangement. NH 3  is formed at least temporarily by chemical reaction by the reducing agent-generating unit from NO x  produced in the NO x  generation step. The invention is applicable in motor vehicles, especially in passenger vehicles with Diesel engines.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention concerns an internal combustion engine with a reducing agent-generating unit and an operating method for the engine.

Non-published German patent application 10128414.4 describes an internal combustion engine with reducing agent-generating unit. The reducing agent-generating unit serves for producing an H₂-containing, and NH₃-containing reducing gas, which can be added upstream of an NO_(x) catalytic converter to the exhaust gas line of the internal combustion engine. An HC-containing (HC=hydrocarbon) fuel, as well as air and/or exhaust gas can be supplied to the reducing agent-generating unit. The generation of the H₂ portion, and the NH₃ portion in the reducing gas takes place in parallel controlled units, which makes the utilization of circuit components and the utilization of an intermediate storage unit necessary.

In contrast, an objective of this invention is to provide an internal combustion engine with a reduction-generating unit and an operating method for this, by means of which reducing agents for effective exhaust gas cleaning can be provided in a manner simple as to construction and process engineering.

This objective is accomplished in accordance with the invention.

The internal combustion engine of the invention includes a reducing agent-generating unit which has an NO_(x) generation step and an H₂ generation step in serial arrangement. The serial arrangement allows for a constructionally simple coupling of the generation steps with a low number of control valves, and independent of each other to a high degree, and therefore an easy to control operation of the generation steps. The NO_(x) produced by the NO_(x) generation step may be reduced as required by reducing the H₂ from the H₂ generation step to NH₃. Hereby, in connection with a suitable exhaust gas catalytic converter, an effective reducing agent for removing the nitrogen oxides present in the exhaust gas of the internal combustion engine is available. The H₂ produced by the H₂ generation step may also be utilized for the catalytic reduction of the nitrogen oxide contents in exhaust gas, especially at low temperatures.

The H₂ generation step is preferably realized as a POX reactor (POX=partial oxidation). By the appropriate selection of the operating conditions of the POX reactor, the composition of the product gas may be purposefully set, so that for example a product gas rich in H₂, or a product gas rich in cracked short-chain hydrocarbons is obtained. Since short-chain hydrocarbons or hydrogen are or is more effective with respect to NO_(x) reducing than long-chain hydrocarbons, especially at low temperatures, a mineral oil used as fuel for the internal combustion engine may be turned into a more efficient reducing agent for nitrogen oxides by means of such a reactor. Furthermore, the various temperature ranges of the effectiveness of the reducing agents producible by the reducing agent-generating unit may also be utilized, and the composition of the reducing gas may be adapted to the temperature of the NO_(x) reducing catalytic converters. An NO_(x) reduction is thereby made possible in a wide temperature range.

The H₂ yield of the H₂ generation may be increased by including a water gas shift reaction (CO+H₂O ---->CO₂+H₂), or by a steam-reforming reaction (HC+H₂O ---->CO₂+H₂). These may also take place in the H₂ generation step, or in a separate a reaction step preferably downstream from the generation step. The water necessary for the run of the water gas shift reaction, or the steam reforming reaction may be added to the relevant educt gas. If exhaust gas is added to the reducing agent-generating unit, the precondition for the run of the water gas shift reaction, or the steam reforming reaction, is already a given because of its water content.

Because of the easy oxidizability of the H₂ produced by the reducing agent-generating unit, in addition a quick heating up of catalytic converters in the exhaust gas string can be achieved. By adding the produced H₂ input of an exhaust gas catalyst, a rapid start-up of this catalytic converter may be achieved, which is of special importance in the reduction of pollutant emission at cold start. Similarly, catalytic converters may be effectively operated under thermally unfavorable conditions, such as in an underfloor position of a motor vehicle.

With the largely self-sufficiently operating reducing agent-generating unit, which is largely independent of the operation of the internal combustion engine, the reducing agent can thereby be made available on board of the associated motor vehicle and utilized for pollutant reduction. Since the reducing agent-generating unit can only be fed by the fuels, which are available on board of the motor vehicle anyhow, additional fuels and their storage become, or intermediate storage becomes, superfluous. Furthermore, the necessity is largely eliminated of converting the operation of the internal combustion engine for providing reducing agents for the NO_(x) reduction, e.g. to a rich combustion, which is associated with difficulties especially in Diesel engines. Overall, therefore, a reduction of the pollutant contents in exhaust gas is made possible in a constructionally simple manner, which is largely independent of the operation of the internal combustion engine.

In a refinement of the invention, the NO_(x) generation step is downstream from the H₂ generation step. This arrangement may offer benefits in the operation of the reducing agent generation. For example, the reducing gas flowing out of the upstream H₂ generation step in a hot state may cool down when passing through the NO_(x) generation step, so that the subsequent components are not being stressed too much thermally.

In a further refinement of the invention, the NO_(x) generation step is upstream of the H₂ generation step. This arrangement may also offer benefits in the operation of the reducing agent generation. For example, the gas flowing out of the upstream NO_(x) generation step may be utilized for controlling the process taking place in the downstream H₂ generation step.

In a further refinement of the invention an NH₃ generation step is arranged downstream from the NO_(x) generation step. The NH₃ generation step serves the on-board generation of NH₃, preferably adjusted to the requirements, so that this reducing agent does not have to be carried in a storage container for NO_(x) reduction.

In a further refinement of the invention, a fractionating unit is arranged to the reducing agent-generating unit in such a way that low-boiling components of a fuel used for operating the internal combustion engine are separable from the fractionating unit, which can be supplied to the H₂ generation step. This embodiment has the advantage that a reducing agent-generating unit realized, for example, as POX reactor, is easier to operate. The low-boiling components separated from the fuel are better and more completely cracked by the POX reactor. Furthermore, the formation of soot and condensation problems in the POX reactor may largely be prevented and the operating temperatures can be reduced. The degree of efficiency and the H₂ yield of the partial hydrocarbon oxidation can also be improved. Furthermore, by the fractioning largely sweet fuel components may be separated. The H₂ generation step is therefore only supplied with low-boiling fuel components, which are free of sulphur, so that sulphur poisoning is minimized.

In a further refinement of the invention, the NO_(x) generation step is operable in two operating modes with the H₂ generation step, such that in the first operating mode of the NO_(x) generation step, an NO_(x)-containing gas can be produced, and in the second operating mode an H₂-containing gas and NH₃-containing gas can be produced by the reducing agent-generating unit. This refinement allows an operation of the reducing agent-generating unit advantageously according to the need. In periods of time during which the component of the reduction gas is not needed, the operation of respective generation unit may be stopped.

In a further refinement of the invention an NO_(x) intermediate storage unit is arranged downstream from the NO_(x) generation step. In this embodiment, the NO_(x) generation step may also be operated with a low degree of efficiency. The NO_(x) available only in small concentrations in the product gas is accumulated in the NO_(x) intermediate storage unit, and after a certain time is available in large amounts for the reaction into NH₃.

In a further refinement of the invention, the NO_(x) intermediate storage unit is designed for the reaction of stored NO_(x) with H₂ into NH₃. With this double function of NO_(x) storage and formation of NH₃, the reducing agent-generating unit can have an especially compact design. In particular a NO_(x) storage catalytic converter may be used as an intermediate NO_(x) storage unit. An NO_(x) storage catalytic converter optimized, for example, by an increased rhodium content, with respect to the function of NO_(x) formation can be used within the framework of the invention.

In a further refinement of the invention, the H₂ generation step is realized for the reaction of the NO_(x) supplied into NH₃. If the H₂ generation step is simultaneously supplied with NO_(x) from the upstream arranged NO_(x) generation step, and HC-containing fuel supplied thereto, in one single, preferably catalytic operation, H₂ as well as NH₃ can be produced. In the partial hydrocarbon oxidation taking place under reducing conditions, the reduction of NO_(x) into NH₃ is preferred due to thermodynamic reasons, because of which this reduction step can be put together in an advantageous fashion in one operation with the H₂ generation. Thus, an NH₃ and H₂-containing reducing gas is produced in one operation. Hereby, the generation of the NH₃ and H₂-containing reducing gas is done preferably continuously.

In a further refinement of the invention, the NO_(x) generation step is designed for the generation of NO_(x) from air and/or oxygen-containing exhaust gas. Preferably, NO_(x) is produced in the NO_(x) generation step in a plasma process by an electric arc, or by a corona discharge. In conjunction with the downstream arranged reduction of NO_(x) thereby NH₃ is exclusively produced from components of the air and the carried fuel, and therefore the storage of an NH₃ releasing substance, such as urea, may be eliminated.

In a further refinement of the invention, the reducing NO_(x) catalytic converter has a denox catalytic converter step for the reaction of NO_(x) with H₂, and an SCR catalytic converter step for the reaction of NO_(x) with NH₃. In both cases, the NO_(x) reduction may take place in lean exhaust gas conditions, which is the reason why the internal combustion engine is preferably operated continuously lean, and so that the full consumption benefit of the lean operation can be taken advantage of. In addition it is possible to benefit from the various temperature ranges of the efficiency of the two catalytic converter steps, which is why an efficient nitrogen oxide reduction can be achieved in a wide temperature range.

The procedure according to the invention is characterized by the following operations:

a) Generation of an NO_(x)-containing gas by one of the NO_(x) generation steps allocated to the reducing agent generating unit from the air and/or exhaust gas supplied to the generation step;

b) Intermediate storage of NO_(x) during the passage of the NO_(x)-containing gas produced during operation a by an NO_(x) intermediate storage allocated downstream to the NO_(x) generation step, and arranged to the reducing agent-generating unit;

c) Generation of an H₂-containing gas by an H₂ generation step allocated to the reducing agent-generating unit and arranged upstream from the NO_(x) intermediate storage unit from fuel, as well as air and/or exhaust gas supplied to the H₂ generation step;

d) Reaction of NO_(x) stored in the NO_(x) intermediate storage unit with the gas produced in generation step cc into NH₃, so that an H₂-containing, and an NH₃-containing reducing gas is produced, whereby the operations a, and b are alternately performed with operations c and d.

With process control according the invention, the NO_(x) generation and NO_(x) intermediate storage unit takes place alternately with the generation of an H₂-containing, reducing gas, release of the intermediately stored NO_(x) and its reduction to NH₃. An H₂/NH₃-containing reduction gas is added intermittently to the reducing catalytic converter. Since, however, preferably an NH₃ storing SCR catalytic converter is employed as NO_(x) reducing catalytic converter, this can nevertheless continuously reduce NO_(x) contained in exhaust gas, since in the operating phases, in which no NH₃ is added to the catalytic converter, NH₃ added in the preceding operating phase and stored is used for NO_(x) reduction. By the NO_(x) intermediate storage unit in the operating phases of the NO_(x) generation, an enrichment of the produced NO_(x) takes place, which when reducing gas with reducing composition is added, is released again in higher concentration from the NO_(x) intermediate storage unit, and turned into NH₃. Therefore, the reducing agent NH₃ can be added to the NO_(x) reducing catalytic converter at a comparatively high concentration.

In refinement of the procedure the NO_(x) reaction into NH₃ takes place in an NH₃ generation step, which is arranged to the reducing agent-generating unit, and arranged downstream to the NO_(x) intermediate storage unit. Preferably the NH₃ generation step contains an NH₃ formation catalytic converter which catalyzes the reductive reaction of NO_(x) into NH₃. A catalytic converter with a very high efficiency with respect to NH₃ formation is for example described in the unpublished German patent application 10214686.1. If NO_(x) and H₂-containing reducing gas is added to such a catalytic converter, a reaction results from NO_(x) to NH₃ from a high percentage.

In a further refinement of the procedure, the intermediate storage of NO_(x), and the NO_(x) reaction to NH₃ is performed by means of a catalytic NO_(x) intermediate storage. The catalytic NO_(x) intermediate storage preferably has an NH₃ formation function in such a way that stored NO_(x) is reduced to NH₃ at least partially under reducing, or stoichiometrical conditions. Such a behavior is shown for example by NO_(x) storage catalytic converters, which are preferably employed here. By the functions of the NO_(x) intermediate storage, and the NH₃ formation integrated into a catalytic component, a compact construction of the reducing agent-generating unit can be achieved.

A further procedure according to the invention is characterized by the following operations:

a) Generation of an NO_(x)-containing gas of an NO_(x) generation step allocated to the reducing agent-generating unit, from air and/or exhaust supplied to the NO_(x) generation step;

b) Generation of an H₂-containing and NH₃-containing reducing gas by an H₂ generation step, allocated to the reducing agent-generating unit and arranged downstream from the NO_(x) generation step, from the NO_(X)-containing gas supplied to the H₂ generation step, fuel supplied, as well as air supplied and/or exhaust gas supplied.

By means of this process control in accordance with the invention, a continuous generation of an H₂-containing and NH₃-containing reducing gas, and its supply to the NO_(x) reducing catalytic converter takes place. Preferably, the H₂ generation step has a catalytic converter with NH₃ formation function, and by the H₂ generation step an H₂-containing and NH₃-containing reducing gas is produced. The H₂ elimination reaction from the HC-containing fuel in the H₂ generation step, and the reduction of the added NO_(x) to NH₃ is performed in the same procedure. Thus an H₂ and NH₃-containing reducing gas is generated in one operation. This advantageously simplifies the realization of the reducing agent-generating unit.

In refinement of the procedures according to the invention in one of the fractioning units arranged to the reducing agent generation unit, a fuel enriched in low-boiling components is produced, which is added to the reducing agent generation unit for the generation of reducing gas. The H₂ generation step is thereby supplied with low-molecular hydrocarbons, whereby its educt gas stream is better homogenized, a change into coke is prevented, and the H₂ yield is increased.

In refinement of the procedures according to the invention the NO_(x) reducing catalytic converter is divided into a denox catalytic converter step for the reaction of NO_(x) with H₂, and into an SCR catalytic converter step for the reaction of NO_(x) with NH₃, and depending upon its composition, the reducing gas is supplied to the exhaust gas on the input side to the SCR catalytic converter step (3 a), or on the input side to the denox catalytic converter step (3 b). Since the catalytic converter steps have different temperature ranges for their effectiveness, and the HC, H₂, NH₃ generated by the reducing agent-generating unit have their optimal effectiveness at various temperatures, a high NO_(x) reduction in exhaust gas can thereby be achieved in a broad temperature range. The denox catalytic converter step may also be designed for the reduction of NO_(x) with HC, which expands the application area of the reducing gas.

In further refinement of the procedure, the amount and/or the composition of the reducing gas generated by the reducing gas generation unit is set as a function of the operating state of the internal combustion engine. Preferably, the reducing agent generation unit provides more reducing gas at high-volume NO_(x) emissions of the internal combustion engine than at low. The procedure is preferably controlled in such a way that the effect of the relevant NO_(x) reducing catalytic converter brings the optimal benefit. At low charge of the internal combustion engine, or low exhaust gas temperature, preferably a reducing gas rich in H₂ is produced. At a higher load of the internal combustion engine, or a higher exhaust gas temperature, the reducing agent-generating unit is preferably operated in such a way that the reducing gas contains more NH₃. Thereby in turn an SCR catalytic converter with higher NO_(x) conversion is operated in the exhaust gas train of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained below in greater detail on the basis of drawings and related examples.

FIG. 1 is a schematic block diagram of an internal combustion engine with reducing agent-generating unit;

FIG. 2 is a schematic block diagram of a construction of a reducing agent-generating unit;

FIG. 3 is a schematic block diagram of the construction of a further embodiment of the reducing agent-generating unit;

FIG. 4 is a schematic block diagram of the construction of a further embodiment of the reducing agent-generating unit;

FIG. 5 is a schematic block diagram of the construction of a further embodiment of the reducing agent-generating unit; and

FIG. 6 is a schematic block diagram of the construction of an embodiment of the reducing agent-generating unit with an allocated fractioning unit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1, an internal combustion engine 1 realized as a four-cylinder Diesel engine is shown here by way of example. In the following, simply the term motor will be used. The exhaust gas produced in the combustion process is conducted to the environment via the exhaust gas line 2. In exhaust gas line 2 here, by way of example the catalytic converter steps 3 a, and 3 b comprising the NO_(x) reducing catalytic converter 3 is arranged.

The catalytic converter step 3 a is realized as SCR catalytic converter, by means of which with NH₃ as reducing agent an NO_(x) reduction takes place under lean exhaust gas conditions. An SCR catalytic converter on a V₂O₅/WO₃/TiO₂ basis as full extrudate, or another catalytic converter suitable for the NO_(x) reduction with NH₃ may be employed. The temperature range of the effectiveness of the catalytic converter step 3 a normally is in the range between 200° C. and 400° C.

The catalytic converter step 3 b is realized as denox catalytic converter, by means of which an NO_(x) reduction takes place under lean exhaust gas conditions with H₂ and/or HC as a reducing agent. Preferably a precious metal-containing catalytic converter is employed, but a Cu substituted zeolite, or another catalytic converter suitable for the NO_(x) reduction with H₂ or HC may also be employed. The temperature range of the effectiveness of the catalytic converter step 3 b, with H₂ as reducing agent, normally is in the range between 80° C. and 200° C., with HC as reducing agent between 180° C. and 400° C.

The reducing agent-generating unit 20 serves for the generation of the reducing agent H₂ and/or NH₃. For this purpose, it may be supplied with fuel, or air, or exhaust gas via the fuel supply line 9, or via the gas supply line 10 as needed. The reducing agent-generating unit 20 has a controlled heating system (not shown), which is mainly operated for start-up. The reducing gas produced by the reducing agent-generating unit 20, may be added to the exhaust gas on the input side of the catalytic converter steps 3 a, 3 b, via the addition line 8, and the addition locations 4, 5.

The operation of the motor, and the operation of the reducing agent-generating unit 20 is controlled by a motor control unit 6, which, for this purpose is connected with the motor 1, or with the reducing agent-generating unit 20 via control lines 7.

Of course, additional components may be arranged to the motor 1, or the exhaust gas system, which are not shown here for reasons of clear grouping. These may especially consist of further catalytic pollution abatement units, a particle filter, and sensors in the exhaust gas line 2, as well as the usual additional motor components such as injection system, exhaust gas turbocharger, components for the exhaust gas return, etc. Also not shown are switchable, or adjustable locking mechanisms in the addition line 8, and the addition lines 9, 10.

The reducing agent unit 20 is now operated in such a way that reducing gas is produced as a function of the NO_(x) emission of the motor 1, and is added to the exhaust gas on the input side of the catalytic converter steps/step 3 a and/or 3 b. For this, in the motor control unit 6, there exist, for example, performance characteristics, in which the NO_(x) emission is laid down as a function of the motor operating point. The procedure of the reducing gas generation is controlled and monitored by the motor control unit 6, whereby the motor control unit 6 has all the necessary information available regarding the reducing gas composition, and the operating status of the reducing agent-generating unit 20.

The motor control unit 6 controls the addition amounts of air, or exhaust gas, as well as fuel, and the operation of the reducing agent-generating unit 20 preferably in such a way, that with a low exhaust gas temperature, reducing gas is mainly supplied to the exhaust gas via the addition location 4 at the inlet of the denox catalytic converter 3 b. The reducing gas generation is hereby controlled in such a way, that the reducing gas predominantly contains H₂ as reducing agent. Thereby, also at low exhaust gas temperatures, or at low temperatures of the catalytic converter step 3 b, an efficient NO_(x) reduction of the motor exhaust gas is achieved. The addition amount of the reducing gas thereby is set by the motor control unit 6 according to the NO_(x) contents of the exhaust gas of the exhaust gas temperature, or the temperature of the catalytic converter step 3 b, as well as the H₂ contents of the reducing gas. Preferably a molar ratio of about 3:1 of H₂:NO_(x) is set at the input side of the denox catalytic converter.

If, with increasing exhaust gas temperature, the catalytic converter step 3 b falls outside of the temperature range of its efficiency, the addition amount of predominantly H₂-containing reducing gas is reduced, or stopped at the addition location 4. At the same time, the operation at the reducing agent-generating unit is changed in such a way that this results in a higher NH₃ portion, and the reducing gas is added to the exhaust gas at addition location 5 at the input of catalytic converter step 3 a. Since with increasing exhaust gas temperature the SCR catalytic converter of the catalytic converter step 3 a becomes gradually more efficient, now the NO_(x) reduction takes place predominantly at this catalytic converter.

At a further continuous increase of the exhaust gas temperature, also the SCR catalytic converter of the catalytic converter step 3 a may come outside of the temperature range of its effectiveness. In this case, the reducing gas generation is changed in such a way that mainly a cracked fuel with short-chain hydrocarbons is produced from the reducing agent-generating unit 20. This reducing gas may then be conducted to the further downstream located, and therefore less hot, denox catalytic converter of catalytic converter step 3 b. At this catalytic converter, at temperatures of about 300° C., an NO_(x) reduction with these hydrocarbons takes place.

Further catalytic converters, which are not shown here, may be arranged in the exhaust gas line 2, which can also be supplied with reducing gas, as needed, via an appropriate addition location. In particular, H₂-containing reducing gas may be apportioned to the exhaust gas at the inlet of a primary catalytic converter arranged near the motor for reducing emissions during a cold start of the motor 1. A rapid heating of the primary catalytic converter can be achieved in this way. As a consequence, pollutants can be removed from the exhaust gas already in an early phase of the motor warm-up period.

FIG. 2 schematically shows the construction of the reducing agent-generating unit 20 in a preferred embodiment. The reducing agent-generating unit 20 here comprises an H₂ generation step 21, an NO_(x) generation step 22, an NO_(x) intermediate storage unit 23, and an NH₃ generation step 24 in serial arrangement. The H₂ generation step 21 can be supplied with fuel at measured volumes via the fuel supply line 9, and air, and/or exhaust gas via the gas supply line 10. The NO_(x) generation step 22 can also be supplied with air, and/or exhaust gas at measured volumes via the gas supply line 10. The means used for measuring the volume are not shown here.

The embodiment of the reducing agent-generating unit 20 represented is preferably operated alternately, so that alternately NH₃ and/or H₂, or NO_(x) are being produced. For producing H₂, the H₂ generation step 21 realized as a catalytic POX reactor, if needed, is first of all warmed-up to operating temperature by means of a not shown electric heater. Hereby, the operating temperature of the catalytic converter arranged in the POX reactor is about 600° C. to 1000° C. Afterwards, the POX reactor is supplied with fuel, and air, or exhaust gas in a weighted flow determined by the motor control unit. Thereby, a air/fuel ratio of preferably about λ =0.3 is set. At this lambda value the partial fuel oxidation in the POX reactor is practically free of soot. The reaction product consists of a reducing gas with a composition, which is highly dependent on the course of procedure, i.e. mainly on the temperature of the POX catalytic converters, and on the air/fuel ratio set. Typical content levels of the reducing agent H₂ or CO are about 18%. The reducing gas may additionally contain a certain content of low-molecular hydrocarbons.

This reducing gas is now conducted through the NO_(x) generation step 22, which is not in operation during this phase of the reducing gas generation. After passing it through the NO_(x) generation step 22, the reducing gas flows through the NO_(x) intermediate storage unit 23, which contains an NO_(x) adsorber. The NO_(x) adsorber may for example be a ceramic honeycomb body, which is coated with a material, which in oxidizing conditions absorbs NO_(x) by adsorption, or absorption, and which releases NO_(x) again in reducing conditions. For this, an NO_(x) adsorber material on a silver basis is suitable, for example. If the NO_(x) intermediate storage unit was loaded with NO_(x) before the reducing gas produced in the H₂ generation step 21 flows through, it is consequently released. The reducing gas enriched with NO_(x) is further conducted to the NH₃ generation step 24. This preferably contains a catalytic converter with a precious metal coating. The reduction of NO_(x) to NH₃ is catalyzed by this catalytic converter, so that finally an NH₃ and H₂-containing reducing gas leaves the reducing agent-generating unit 20 via the reducing gas line 8, and is added at one, or both of the addition locations 4, 5 to the exhaust gas of the motor 1 (see FIG. 1).

If the NH₃ formation comes to a halt, for example by exhaustion of the amount of NO_(x) stored in the NO_(x) intermediate storage unit, if needed, the operation of the reducing agent-generating unit 20 for producing NO_(x) can be switched. For this purpose, the supply of air, or exhaust gas, as well as the supply with fuel to the H₂ generation step 21 is stopped. Subsequently, the NO_(x) generation step 22 is supplied with air and/or oxygen-containing exhaust gas. In the NO_(x) generation step 22 thereupon for example a plasma process is started, or an electric arc, or a corona discharge is ignited. By such a process NO_(x) is produced in the nitrogen and oxygen-containing atmosphere of the NO_(x) generation unit. Preferably an NTP procedure (NTP=non-thermal plasma) is started, and maintained for the desired time of the NO_(x) generation. The NO_(x) produced by means of this process has a high NO₂ portion of normally over 50%, which improves the subsequent storage after the supply of the generation gas to the NO_(x) intermediate storage unit 23. As described above, in this situation the supplied NO_(x) is to be absorbed by adsorption, or by absorption. The NO_(x) free gas is further conducted through the NH₃ generation step, from where it is added essentially unchanged to the exhaust gas of the motor 1 via the reducing gas line 8 at one of the addition locations 4, 5 (see FIG. 1). If the NO_(x) intermediate storage unit 23 is saturated with NO_(x), or if the supply of reducing gas to a catalytic converter step is required for other reasons, the generation of NO_(x) is stopped, and the generation of reducing gas with a reducing effect as described above again takes place.

FIG. 3 schematically illustrates the construction of the reducing agent-generating unit 20 in a further preferred embodiment. The designation and the function of the of the components with the same effectiveness, corresponds to FIG. 2. As compared to the embodiment shown in FIG. 2, the reducing agent-generating unit 20 shown in FIG. 3 differs in the exchange of the H₂ generation step 21, and the NO_(x) generation step 22. Also the embodiment of the reducing agent-generating unit shown in FIG. 3 is preferably operated alternately such, that alternately H₂ and/or NH₃ are produced, or NO_(x) is produced. In the operating phases with NO_(x) generation, however, in turn the H₂ generation step 21 is not in operation, and the NO_(x)-containing product gas of the NO_(x) generation step 22 flows through the H₂ generation step 21. Thereby, in the warmed-up H₂ generation step 21 a regeneration of coking possibly caused by the cracking process may occur, which improves the operatability of the POX catalytic converter. Analogous to the function of the embodiment shown in FIG. 2, NO_(x) is withdrawn from the gas in the NO_(x) intermediate storage unit 23 by storage. After switching the operation of the reducing agent-generating unit 20 by terminating the NO_(x) generation, and starting operation of the H₂ generation step 21, reducing H₂-containing reducing gas flows through the NO_(x) intermediate storage unit 23, whereby the release of the stored NO_(x) takes place, as described above. In the downstream arranged NH₃ generation step 24 thereupon a reaction of the stored NO_(x) into NH₃ takes place, and the reducing gas is enriched with NH₃. The produced reducing gas is, as described above, fed as needed at the inlet of a catalytic converter step into the exhaust gas line.

FIG. 4 schematically shows the construction of a reducing agent-generating unit 20 in a further preferred embodiment. Analogous to the embodiments in FIG. 2, and FIG. 3, this variation is also operated alternately. The differences in construction and in their function as compared to the embodiments in FIGS. 2 and 3 are described in the following. To the NO_(x) generation step 22, here an NO_(x) storage catalytic converter step 26 is arranged downstream, which at the same time fulfills the function of the NO_(x) intermediate storage unit and the NH₃ formation. In the supply of reducing reducing gas from the H₂ generation step 21 to the NO_(x) storage catalytic converter step 26, the NO_(x) which is stored there gets released and at the same time NH₃ gets reduced. This effect, which occurs in the usual NO_(x) storage catalytic converters, can be utilized advantageously. Preferably in this step 26 an NO_(x) storage material is employed, which, with respect to the NH₃ formation is for example optimized by an increased rhodium content. A further simplification is achieved in that the gas necessary for the generation of NO_(x) is supplied to the NO_(x) generation step 22 via the H₂ generation step 21; therefore a branching of the gas supply line 10 can be eliminated. In comparison to the embodiments in FIG. 2 and FIG. 3 components can be eliminated hereby, whereby the reducing agent-generating unit 20 can be realized in a simpler way.

FIG. 5 schematically shows the construction of the reducing agent-generating unit 20 in a further preferred embodiment. As explained in the following, this embodiment can be operated on a continuous basis, i.e. the NO_(x) generation and NH₃ generation can take place simultaneously. For this purpose a reactor step 25 is provided, in which simultaneously an H₂ generation, preferably by a catalytic partial oxidation process, and a reduction of the NO_(x) supplied to the NO_(x) generation step 22, can take place. The NO_(x) generation thereby is performed as described in the above embodiments. The necessary educt gas is supplied to the NO_(x) generation step 22 via the gas supply line 10 as needed. The gas supply line additionally may have a branch for reactor step 25. The reactor step 25 is supplied with hydrocarbon-containing fuel via the supply line 9. Preferably in the operation of reactor step 25 an air/fuel ratio of about λ=0.3 is set there. In this way, the thermodynamically preferred conditions are present, on the one hand for the H₂ generation by partial oxidation, and on the other hand for the reduction of NO_(x) to NH₃, so that H₂ as well as NH₃ can be produced in one process. The volume ratio of these two components thereby can be set as needed by the appropriate setting of fuel, or NO_(x) supplied to reactor step 25.

FIG. 6 schematically shows the construction of the reducing agent-generating unit 20 in a further preferred embodiment. The reducing agent-generating unit 20 contains, analogous to the embodiment shown in FIG. 4, an H₂ generation step 21 arranged downstream to the NO_(x) generation step 22. The furthermore downstream arranged NO_(x) storage catalytic converter step 26 serves for the NO_(x) intermediate storage and NH₃ generation. The system is preferably operated in altering generation phases, and H₂, or NH₃ generation phases. For the generation of NO_(x), the NO_(x) generation 22 is supplied with air and/or exhaust gas via the gas supply line 10. Via a branch-off, the H₂ generation step 21 can be supplied with air and/or exhaust gas as well. To the reducing agent-generating unit 20 furthermore a fractioning unit 27 is arranged to, in which from the fuel provided for the motor operation, low-boiling components are separated off in a fractioning process. For this purpose the fractioning unit 27 is supplied with fuel from the storage container of a motor not shown here, via the fuel supply line 9. Via the return line 9 b the fuel enriched in low-boiling components is returned again. The separated low-boiling fuel components are conducted to the H₂ generation step 21 for H₂ generation via the fuel supply line 9 a. By the fact, that the H₂ generation step 21 is operated with low-boiling hydrocarbons, the H₂ generation can take place with a higher yield, and the danger of coking of the POX catalytic converter is reduced. In addition, the possibility exists for preparing the low-boiling fuel components when needed only at low levels, and to add to the lean exhaust gas on the input side of a denox catalytic converter. Therefore, in the temperature range of about 200° C. to 350° C. an efficient NO_(x) reduction may be achieved. To increase the H₂ yield in the generation of reducing gas, the reducing agent-generating unit 20 can generally be supplied with additional water. The water can thereby be taken from a storage container of the associated motor vehicle, or be obtained by condensation from the motor exhaust gas. The water may, for example be utilized for a steam reforming process in the H₂ generation step 21. Apart from the increase of the H₂ content in the produced reducing gas this brings the additional advantage, that this endothermal process improves the heat and energy balance of the H₂ generation. Furthermore a larger range for temperature management in the H₂ generation step 21, and the complete reducing agent-generating unit 20 is gained. The water may, however, also be supplied to a water gas shift step arranged downstream from the H₂ generation step 21. The thereby with H₂ enriched reducing gas has a higher selectivity in the NH₃ generation, and in the NO_(x) reduction at a denox catalytic converter. At the same time the CO contents is reduced in the reducing gas, which prevents a poisoning of the denox catalytic converter by CO accumulation of active catalytic centers.

It is obvious that to the reducing agent-generating unit 20 heat exchangers may be arranged to, in order to improve the heat and energy balance of the total process, and the course of the procedure. Thus, for preheating of the supplied air, or the supplied exhaust gas for example, a heat exchanger may be provided in the gas supply line 10. Heat exchangers may, however, also be provided in the reducing agent-generating unit 20, for example in order to utilize the heat content of the hot product gas flow of the H₂ generation step, or the NH₃ generation step for preheating of the educt gas of a preliminary step. 

1-18. (canceled)
 19. An internal combustion engine comprising: an exhaust gas line in which an NO_(x) reduction catalytic converter is arranged, and a reducing agent-generating unit for generation of H₂-containing and NH₃-containing reducing gas which can be added upstream of the NO_(x) reduction catalytic converter in the exhaust gas line, wherein the reducing agent-generating unit can be supplied with at least one of an HC-containing fuel, air, and exhaust gas, and wherein the reducing agent-generating unit has an NO_(x) generation step and an H₂ generation step in serial arrangement.
 20. The internal combustion engine according to claim 19, wherein the NO_(x) generation step is arranged downstream from the H₂ generation step.
 21. The internal combustion engine according to claim 19, wherein the NO_(x) generation step is arranged upstream from the H₂ generation step.
 22. The internal combustion engine according to claim 19, further comprising an NH₃ generation step arranged downstream from the NO_(X) generation step.
 23. The internal combustion engine according to claim 20, further comprising an NH₃ generation step arranged downstream from the NO_(X) generation step.
 24. The internal combustion engine according to claim 21, further comprising an NH₃ generation step arranged downstream from the NO_(X) generation step.
 25. The internal combustion engine according to claim 19, wherein the reducing agent-generating unit can be operated alternately in first and second operating modes in such a way that, during the first operating mode, an NO_(X)-containing gas can be produced and, during the second operating mode, an H₂-containing and NH₃-containing reducing gas can be produced.
 26. The internal combustion engine according to claim 22, wherein a reducing agent-generating unit can be operated alternately in first and second operating modes in such a way that, in the first operating mode, an NO_(X)-containing gas can be produced and, in the second operating mode, an H₂-containing and NH₃-containing reducing gas can be produced.
 27. The internal combustion engine according to claim 23, wherein a reducing agent-generating unit can be operated alternately in first and second operating modes in such a way that, in the first operating mode, an NO_(X)-containing gas can be produced and, in the second operating mode, an H₂-containing and NH₃-containing reducing gas can be produced.
 28. The internal combustion engine according to claim 24, wherein a reducing agent-generating unit can be operated alternately in first and second operating modes in such a way that in the first operating mode of the NO_(X) generation step, an NO_(X)-containing gas can be produced and, in the second operating mode, an H₂-containing and NH₃-containing reducing gas can be produced.
 29. The internal combustion engine according to claim 25, further comprising an NO_(X) intermediate storage unit arranged downstream from the NO_(X) generation step.
 30. The internal combustion engine according to claim 26, further comprising an NO_(X) intermediate storage unit arranged downstream from the NO_(X) generation step.
 31. The internal combustion engine according to claim 27, further comprising an NO_(X) intermediate storage unit arranged downstream from the NO_(X) generation step.
 32. The internal combustion engine according to claim 28, further comprising an NO_(X) intermediate storage unit arranged downstream from the NO_(X) generation step.
 33. The internal combustion engine according to claim 29, wherein the NO_(X) intermediate storage unit is designed for reaction of stored NO_(X) with H₂ to NH₃.
 34. The internal combustion engine according to claim 30, wherein the NO_(X) intermediate storage unit is designed for reaction of stored NO_(X) with H₂ to NH₃.
 35. The internal combustion engine according to claim 31, wherein the NO_(X) intermediate storage unit is designed for reaction of stored NO_(X) with H₂ to NH₃.
 36. The internal combustion engine according to claim 32, wherein the NO_(X) intermediate storage unit is designed for reaction of stored NO_(X) with H₂ to NH₃.
 37. The internal combustion engine according to claim 21, wherein the H₂ generation step is designed for reaction of supplied NO_(X) into NH₃.
 38. The internal combustion engine according to claim 24, wherein the H₂ generation step is designed for reaction of supplied NO_(X) into NH₃.
 39. The internal combustion engine according to claim 28, wherein the H₂ generation step is designed for reaction of supplied NO_(X) into NH₃.
 40. The internal combustion engine according claim 32, wherein the H₂ generation step is designed for reaction of supplied NO_(X) into NH₃.
 41. The internal combustion engine according claim 36, wherein the H₂ generation step is designed for reaction of supplied NO_(X) into NH₃.
 42. The internal combustion engine according to claim 19, wherein the engine is a Diesel engine.
 43. A process for operation of an internal combustion engine having a reducing agent-generating unit and an exhaust gas line in which an NO_(X) reduction catalytic converter is arranged, whereby a reducing gas produced by the reducing agent-generating unit is added upstream of the NO_(X) reducing catalytic converter to the exhaust gas, wherein generation of the reducing gas comprises: generating an NO_(X)-containing gas from an NO_(X) generation stage allocated to the reducing agent-generating unit from at least one of air and exhaust gas supplied to the NO_(X) generation stage; and intermediately storing NO_(X) when conducting the NO_(X)-containing gas produced through an NO_(X) intermediate storage unit which is arranged downstream from the NO_(X) generation stage and allocated to the reducing agent-generating unit; or generating an H₂-containing gas by an H₂ generation stage allocated to the reducing agent-generating unit and arranged upstream from an NO_(X) intermediate storage unit from fuel and air or exhaust gas supplied to the H₂ generation stage; and reacting NO_(X) stored in the NO_(X) intermediate storage unit with the gas produced into NH₃ so that a reducing gas containing H₂ and NH₃ is produced.
 44. The process according to claim 43, wherein reaction of NO_(x) into NH₃ takes place in the catalytic NH₃ generation stage, which is allocated to the reducing agent generation unit and arranged downstream from the NO_(X) intermediate storage unit.
 45. The process according to claim 43, wherein intermediate storage of NO_(X) and reaction of NO_(X) into NH₃ is performed with a catalytic NO_(X) intermediate storage unit.
 46. The process according to claim 43, wherein the NO_(X) reducing catalytic converter is divided into a denox catalytic converter stage for reaction of NO_(X) with H₂ and an SCR catalytic converter stage for reaction of NO_(X) with NH₃, and wherein the reducing gas is supplied to the exhaust gas as a function of its composition at an input side to the SCR catalytic converter stage or on an input side to the denox catalytic converter stage.
 47. The process according to claim 44, wherein the NO_(X) reducing catalytic converter is divided into a denox catalytic converter stage for reaction of NO_(X) with H₂ and an SCR catalytic converter stage for reaction of NO_(X) with NH₃, and wherein the reducing gas is supplied to the exhaust gas as a function of its composition at an input side to the SCR catalytic converter stage or on an input side to the denox catalytic converter stage.
 48. The process according to claim 45, wherein the NO_(X) reducing catalytic converter is divided into a denox catalytic converter stage for reaction of NO_(X) with H₂ and an SCR catalytic converter stage for reaction of NO_(X) with NH₃, and wherein the reducing gas is supplied to the exhaust gas as a function of its composition at an input side to the SCR catalytic converter stage or on an input side to the denox catalytic converter stage.
 49. A process for operation of an internal combustion engine having a reducing agent-generating unit and an exhaust gas line in which an NO_(X) reduction catalytic converter is arranged, whereby a reducing gas produced by the reducing agent-generating unit is added upstream from the NO_(X) reducing catalytic converter to the exhaust gas, wherein generation of the reducing gas comprises: generating an NO_(X)-containing gas from an NO_(X) generation stage allocated to the reducing agent-generating unit from at least one of air and exhaust gas supplied to the NO_(X) generation stage; and generating an H₂-containing gas and an NH₃-containing reducing gas from an H₂ generation stage allocated to the reducing agent-generating unit and arranged downstream from the NO_(X) generation stage based on fuel fed to the H₂ generation stage, NO_(X)-containing gas produced, fuel supplied, and at least one of air and exhaust gas.
 50. The process according to claim 49, wherein the NO_(X) reducing catalytic converter is divided into a denox catalytic converter stage for reaction of NO_(X) with H₂ and an SCR catalytic converter stage for reaction of NO_(X) with NH₃, and wherein the reducing gas is supplied to the exhaust gas as a function of its composition at an input side to the SCR catalytic converter stage or on an input side to the denox catalytic converter stage. 